1. Field of the Invention
The present invention relates generally to the field of systems for detecting liquids on beds, and more specifically to a urine detecting sensor circuit printed on bed pads and bed sheets, diapers and diaper inserts, including a sheet of material having on its upper surface a pair of spaced apart and parallel strips of metallic material, each strip removably connected to a terminal of an alarm circuit with a snap fastener or magnet fastener, the bed pad having a bottom layer of waterproof material, an absorbent middle layer on which the parallel strips would be printed, and a cloth top layer, such that urine deposited on the bed passes through the top layer and soaks the middle layer, providing both the liquid medium and electrolytes necessary to conduct a small electric current between the metallic strips and activate the alarm, and optionally including heat sensors to indicate departure of a patient from his bed, or to indicate wetness or the presence of a high level of moisture by monitoring the temperature differential between two spaced apart sensors.
2. Description of the Prior Art
There have long been wet bed monitoring systems for sounding an alarm when a person urinates on a bed. These systems may sound the alarm when urine is present, but are often so sensitive that they sound false alarms when exposed to even a minute volume of virtually any liquid. They also tend to be difficult and expensive to manufacture and highly labor intensive to routinely clean.
Examples of such a prior art system include those of Wilson, U.S. Pat. No. 4,356,479, issued on Oct. 26, 1982, and Wilson U.S. Pat. No. 4,271,406, issued on Jun. 2, 1981. Both Wilson devices feature electrodes fabricated from permanent magnets which are held apart by a thin spacer. These magnets are attached to a patient's clothing or bed sheet. Urine completes the circuit between the electrodes to sound an alarm. A problem with Wilson is that the extent of the monitored area when a magnet is attached to a bed sheet is limited to the dimensions of the magnet, and if a patient happens to roll away from that spot and urinates elsewhere, the condition goes undetected. There is also some risk of danger from electric shock where the preferred embodiment including alternating current and the fuse system is employed. Finally, patient mobility is restricted where the option of attachment to the patient's garment is used, because the apparatus must be removed each time the patient gets out of bed.
Regal, U.S. Pat. No. 4,163,449, issued on Aug. 7, 1979, teaches a device which provides an aversive stimulus to a child who bed wets while asleep. Regal includes a urine detection pad of absorbent material having wire screen electrodes on either side of the pad which trigger an alarm when even a small amount of urine is present. A problem with Regal is that the sensor pad would react to any liquid, such as pure water, if soaking causes the wire screens to engage each other. Another problem with Regal is that it is designed to condition a child with an unpleasant sound rather than to alert a nurse or other health care worker at a distance.
Bloom, U.S. Pat. No. 3,971,371, issued on Jul. 27, 1976, discloses a urine sensing pad including a sheet of flexible insulating material carrying an array of conductive sensor strips on both of its faces. Moisture makes the electrical connection between the sensor strips to activate an alarm. A problem with Bloom is that the sensor strips are formed of aluminum tape and fastened to a Mylar pad with staples, which is a fragile construction. Cleaning such an arrangement is difficult, because urine seeps between the pick-up strips and sensor strips. Bacteria can be secluded among the layers, causing potential health problems. Another problem with Bloom is its complicated construction.
Campbell, U.S. Pat. No. 2,907,841, issued on Oct. 6, 1959, discloses a flexible support of dielectric material having crosswise electrodes traversing the width of the support. Alternate crosswise electrodes are attached to the different terminals of the circuit and the circuit is completed when an electrolyte shorts these electrodes, activating an alarm. A problem with Campbell is that free flowing urine is used to activate the device, so that the user must lye in this unabsorbed wetness until help arrives. Campbell is also cumbersome to build, uncomfortable to sleep on because nothing cushions contact with the electrodes and support, and it is difficult to clean. The metal foil is vulnerable to damage from rough handling.
McKenzie, U.S. Pat. No. 2,866,454, issued on Dec. 30, 1958, teaches metal grids of bronze wire; a plastic sheet and a pad to deliver shock treatment to a patient. A problem with McKenzie, apart from its design to shock rather than merely signal, is that it is clumsy and of intricate construction. Low reliability and high manufacturing costs are likely.
Seiger, U.S. Pat. No. 2,644,050, issued on Jun. 30, 1953, discloses a flat, thin, waterproof electro-insulative pad having embedded in its top face several thin metal conductors forming separated electrodes. The presence of urine shorts the electrodes and activates a signal. A problem with Seiger is that moisture is retained against the patient's skin while the signal is triggered. Another problem is that the caustic urine would quickly corrode the rubber and tin materials. Still another problem is that urine would seep into all the many crevices and make cleaning difficult and time consuming.
Kroening, U.S. Pat. No. 2,726,294, issued on Dec. 6, 1955, teaches two elongated flat thin plates of cardboard material, having metallic coatings on either side of the material. A problem with Kroening is that it would be difficult to clean urine from this multi-layer construction. Single use followed by disposal, on the other hand, would make Kroening prohibitively expensive to use. Another problem is that it is cumbersome to build and uncomfortable to sleep on.
Norton, U.S. Pat. No. 5,137,033, issued on Aug. 11, 1992 teaches a patient monitoring device which signals a health care worker with an alarm if moisture is detected. A problem with Norton is that it has numerous wires and is cumbersome. Another problem with Norton is that a nurse's aid has to manually wash and disinfect the pad, which is costly in work time and unpleasant. Additionally, a cloth insert has to be laundered after each use.
It is thus an object of the present invention to provide a moisture monitoring system which is activated only by urine and a limited number of other liquids.
It is another object of the present invention to provide such a monitoring system which is comfortable and which draws urine away from the user to minimize irritating contact with the skin.
It is a further object of the present invention to provide a temperature monitoring system with a single heat sensor which is activated by a fever level temperature of a patient or by a temperature level which indicates patient discomfort.
It is a further object of the present invention to provide a temperature monitoring system, optionally incorporating two heat sensors, which measures the temperature differential between the two heat sensors to detect wetness or a high degree of moisture.
It is still another object of the present invention to provide such a monitoring system which is durable and easily cleaned for reuse.
It is finally an object of the present invention to provide such a monitoring system which is comparatively simple in design and inexpensive to manufacture.